The health department warned the public of the toxin on March 7 after the California Department of Public Health found extremely high levels in a mussel sample from Chimney Rock in the Point Reyes National Seashore.

The department said the sample contained about 37 times the "alert" level of paralytic shellfish poison, known as PSP.

Changes in water conditions, including temperature, flow and salt content can cause the toxins to surge. Symptoms of poisoning could include tingling, numbness, dizziness, nausea, or respiratory problems.

According to the department, the amount of toxins is the highest that Marin has seen in 20 years and could potentially be lethal.

The highest levels were found near Chimney Rock and areas north of Stinson Beach.

They advised the public on March 7 to avoid collecting shellfish until it is safe again.

The warning does not apply to commercially sold clams, mussels, scallops, or oysters from approved sources, the department said.

In the last 90 years, California state statistics say there have been 542 reported illnesses and 39 deaths due to paralytic shellfish poison.